[geos-devel] [GEOS] #241: GEOSBuffer produces an invalid geometry

GEOS geos-trac at osgeo.org
Thu Mar 19 12:49:49 EDT 2009

#241: GEOSBuffer produces an invalid geometry
 Reporter:  pleroux     |       Owner:  geos-devel at lists.osgeo.org
     Type:  defect      |      Status:  new                       
 Priority:  major       |   Milestone:  3.1.1                     
Component:  Default     |     Version:  3.0.0                     
 Severity:  Unassigned  |    Keywords:                            
 Here's a a valid polygon for which the GEOSBuffer function produces an
 invalid geometry.

 At the beginning, I didn't test the returned geometry but only wrote it in
 WKT format (and it "worked"). I tested different values for dist (1 (m)
 and 2) and, with 1, it is obvious than the result is not valid (a big hole
 of the poygon disappears and two small polygons are created). With 2, it
 "seems" good and the obvious error obtained with 1 don't occur any more.

 Even if they are not valid, I think they're interesting to investigate

 >>> from shapely.wkb import loads
 >>> polygon =
 >>> polygon.is_valid
 >>> buffer_1 = polygon.buffer(1.)
 >>> buffer_1.is_valid
 >>> buffer_2 = polygon.buffer(2.)
 >>> buffer_2.is_valid
 >>> print >> open('buffer_1.hexwkb','w'), buffer_1.wkb.encode('hex')
 >>> print >> open('buffer_2.hexwkb','w'), buffer_2.wkb.encode('hex')

 On MacOSX, libgeos 3.0.0, with an equivalent code in C, the problem occurs

Ticket URL: <http://trac.osgeo.org/geos/ticket/241>
GEOS <http://geos.refractions.net/>
GEOS (Geometry Engine - Open Source) is a C++ port of the Java Topology Suite (JTS).

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